Comparison of physico-chemical and rheological characteristics of natural honeys with adulterated and sugar honeys

Honey is a natural food product having a high nutritional and medicinal value. It is a sweet, viscous substance produced by the honeybees from the nectar of plants. Sensory and physical properties and chemical composition of honey depend on the botanical origin and the regional and climatic conditions of the area in which it is produced.The knowledge of honey rheology is very important for its processing, quality control, process control, and selection of proper process equipment, storage, handling, and transportation and plays an important role in fluid heat transfer. Rheological properties of honeys depend on many factors including composition, temperature, and amount and size of crystals. Different kinds of honeys with various floral origins (such as Rosa, Thyme, Astragalus, Trifolium, sunflower, Medicago, alfalfa and etc.) are produced in different regions of Iran. In this study, some physicochemical and rheological properties of four Iranian honeys from Golestanprovienceobtained from various floral sources, two poly floral (Mountain, Forest) and two mono floral (Sunflower, Ivy) were compared with adulteratedand sugar honeys.

Sixhoney samples were collected directly from beekeepers in Golestan Province,two monofloral (Sunflower, Ivy) and two polyfloral(Mountain, Forest), adulterated and sugar honeys. Some physico–chemical characteristics of samples including water content, Hydroxymethylfurfural content (HMF), diastase activity, pH, ash, free acidity, reducing sugars (fructose and glucose), sucrose contentand electrical conductivity were determined by the harmonized methods of the International Honey Commission. The rheological measurements were also carried out on the honey samples at eighteen rotations, ranging from 5-200 rpm and at five temperatures, ranging from 10-30ºC, using a viscosimeter Brookfield.

The samples were found to be different from each other in terms of physico-chemical properties. In the natural honey samples, this discrepancy can be due to diversity in original plant and harvesting season. All the values obtained in the natural honey samples were agreement with those reported by Codex Alimentarius and ISIRI. The values of sucrose and fructose/glucose ratio the sugar honey sample and sucrose, fructose/glucose ratio, pH, HMF, diastase activity of adulterated honey were not in the range suggested by Codex Alimentarius and ISIRI.

Rheological characteristics of honeys were evaluated at different temperatures (10, 15, 20, 25 and 30ºC). All the honeys exhibited Newtonian behavior for shear rate in range of 1.045- 41.8 s-1.The temperature dependence of viscosity was described using the Arrhenius and the Vogel–Taumman–Fulcher (VTF) equations.Two models (Power Law and Exponential models) were also investigated to describe the concentration (ºBrix) dependence of viscosity.